Back to your husband and his partner selection. Set boundaries where you do not share the same space or hear about his other toxic relationships and leave it to him. If he absolutely cannot manage to stop his relationships negatively affecting each other because he chooses toxic partners, that is something you might want to take up with him.

If I was poly and married, felt splitting absolutely wasn't an option but my husband continued to let my toxic metamours affect us, or he couldn't stick to agreements about how we prevent harm to our relationship, the only viable option would be to close the relationship. If I feel the only way to stop it was to actively manage his other relationships by imposing restrictions and setting the pace, I would opt for closing the relationship to work on us.

Just to reiterate that I've spoken about the trust and control issues.